Double metal cyanide (DMC) compounds are known catalysts for epoxide polymerization, i.e. for polymerizing alkylene oxides such as propylene oxide and ethylene oxide to yield poly(alkylene oxide) polymers, also referred to as polyether polyols. The catalysts are highly active, and give polyether polyols that have low unsaturation compared with similar polyols made using strong basic catalysts like potassium hydroxide. In addition to the preparation of polyether polyols, the catalysts can be used to make a variety of polymer products, including polyester polyols and polyetherester polyols. The polyols can be used to prepare polyurethanes by reacting them with polyisocyanates under appropriate conditions. Polyurethane products that can be made include polyurethane coatings, elastomers, sealants, foams, and adhesives.
WO 98/40162 describes a process for making double metal cyanide catalysts by reacting an aqueous solution of potassium hexacyanocobaltate, tert-butyl alcohol and an aqueous solution of zinc chloride in which the alkalinity of the aqueous solution of zinc chloride is about 0.2 to 2.0% wt of zinc oxide based on the amount of zinc chloride in the solution, most preferably from about 0.4 to about 0.9% wt. An amount of zinc oxide of 1.13% wt (Example 7) is considered too high: the polyols obtained had increased unsaturation and increased viscosity. 1.13% wt of zinc oxide corresponds with 0.019 mole of zinc oxide per mole of metal salt.
In addition to higher catalyst activity, it would be useful to produce a polyol containing a lower amount of ultra-high molecular weight compounds as these compounds may have deleterious effects on foam processing when the polyols containing them are used for foam manufacturing purposes.